The present invention relates to a tool for installation of a terminal stud adapter in a generator rotor to effect an electrical connection between field windings and exciter or slip rings and particularly relates to a tool for and methods of installing a terminal stud adapter section of a sectional terminal stud, either as an original equipment manufacture or as a retrofit in a dynamoelectric machine.
The rotors of dynamoelectric machines typically. comprise relatively large diameter cylindrical bodies containing field windings for producing magnetic flux which in turn produces stator current and voltage. These field windings are normally carried in a series of longitudinal slots along the outer circumference and extend the length of the rotor body. Rotation of the body particularly at speeds of 3600 rpm, for example, exerts high centrifugal forces on the windings. These windings are conventionally retained in the rotor slots through the use of dovetail shaped wedges which also extend along the length of the rotor body. The manner in which the windings and rotor slots are shaped, insulated and cooled present formidable design problems, particularly for units designed for long term operation under variable load and environmental conditions. Because the windings extend axially beyond the rotor body and wedge ends and are subjected to the same rotational forces which tend to thrust the winding end turns in a radially outward direction, specially designed structure must be included to make electrical connections between the exciter or slip rings and the windings.
In a current long-standing design affording electrical connection between a field winding and a bore conductor (see, for example, U.S. Pat. No. 5,358,432), a main terminal, i.e., a terminal stud, is inserted into a radial bore of the rotor. The main terminal has tapered threads at its radial inner end for engaging female tapered threads in the bore connector, also known as the xe2x80x9cbore copperxe2x80x9d (insulated conductors embedded in small diameter shafts that extend from opposite ends of the rotor body for electrical connection with the exciter/rectifier assembly). Tolerances of the taper angle, thread pitch, the contacts along major and minor threaded diameters and the need to torque the main terminal to a predetermined value render the installation of the main terminal to bore connector connection difficult as well as affording less than optimal conditions for good electrical connection. The opposite end (radially outer end) of the main terminal includes a plurality of flexible, preferably copper, leaves which are electrically connected to the field winding. Because of the pipe thread type securement between the main terminal and bore connector, the thin terminal leaves are necessarily formed and brazed together at their ends and to the field windings at the generator site. In that process, care must be taken not to melt the necessary thin copper leaves or to allow the brazing alloy to migrate into the flexible part of the terminal. Field brazing of the leaves to one another and to the field winding is time consuming and laborious. Should the leaves melt in the course of brazing or should braze alloy migrate to the flexible part of the terminal, the high rotational and thermal forces of the rotor will cause the flexible connection to prematurely fail causing unscheduled outages and generator down time.
In a companion application of assignee hereof Ser. No. 09/741,160, the disclosure of which is incorporated herein by reference), there is disclosed apparatus and methods for retrofitting generators in the field without the need for remanufacturing or removal of the bore connector from the center of the rotor. To accomplish this, there is provided a sectional main terminal or terminal stud including a radially inner stud adapter section and an outer terminal stud section. The adapter section has on its radially inner end a radially inner, male threaded portion to match the female threaded portion of the existing bore copper, whereby the stud adapter section can be threaded into the bore copper in the field. However, the stud adapter section requires installation at the base of the radial bore of the rotor, the radial bore being less than one and one-half diameters greater than the adapter section and four times longer than the adapter section. Additionally, the adapter section is constructed of a softer material, i.e., copper, than that of the walls of the radial bore and has coated threads, preferably silver-coated, to form a good electrical connection. These threads should not be marred or scraped during installation. Further, the adapter section at the base of the radial bore requires engagement and tightening to a predetermined torque value to afford good electrical connection. The opposite end of the adapter section from the male threads includes a recess for receiving an annular spring-like electrical connector. The outer section includes a radial inner end receivable within the annular spring connector to afford good electrical connection between the outer and adapter sections of the terminal stud. The opposite end of the outer section includes the leaf copper for connection to the field windings. With that arrangement, however, there is a need for a tool to facilitate installation of the terminal stud adapter section both as original equipment in the field as well as a method of installing the sectional terminal stud into the radial bore of the rotor.
In accordance with a preferred embodiment of the present invention, there is provided a tool for inserting and removing the terminal stud adapter section, either as original equipment or in the field, such that the stud adapter section can be threaded to the female threaded aperture of the bore copper at the base of the radial bore of the rotor. To accomplish this, there is provided an elongated, generally cylindrical tool, preferably formed of steel, having at one end a pair of pins projecting from an end face and lying on a diameter. A layer of copper material is disposed about the one end of the tool adjacent the pins. The copper-layered end of the tool is sized and configured for reception in the recess of the adapter section with the pins in apertures at the base of the recess such that the adapter section can be frictionally retained on the end of the tool. The opposite end of the tool may have a head specifically configured for engagement by a driving tool. For example, the head may comprise a series of flat surfaces, e.g., a hex head, for receiving a wrench. Alternatively, a diametrical hole or a longitudinal slot may be provided in the head to accommodate a driving member in the form of a rod and a screwdriver, respectively.
To use the tool, the sectional terminal stud may be deployed as part of original equipment or as a retrofit into existing generators in the field. The rotor end cap and field windings are either not assembled as the case of original equipment or are removed prior to installation of the stud adapter section during a retrofit. For a retrofit, the existing one-piece terminal stud is unthreaded from the female threads of the bore copper and removed. To install the adapter section, one end of the tool is inserted into the recess of the adapter section in frictional engagement with the multi-contact-electrical connector which exerts a bias against the tool whereby the adapter section is frictionally retained on the end of the tool. The adapter section and tool.are then inserted into the bore copper. The driving member is then applied to the driving head of the tool to thread the adapter section onto the female threads of the bore copper. Once the adapter section has been torqued down to a predetermined value, the tool is withdrawn from the recess of the adapter section and the outer section of the terminal stud is inserted into the bore with its inner end received in the recess in electrical contact with the multi-contact-electrical connector. A male threaded nut is threaded into the radial bore of the rotor to maintain the sectional terminal stud in place.
In a preferred embodiment according to the present invention, there is provided a tool for inserting a terminal stud adapter section in a generally radially extending bore hole in the rotor of a dynamoelectric machine for connection to a bore copper, the stud adapter section having a plurality of off-axis apertures opening through one end thereof, comprising an elongated tool body having an axis, a pair of pins projecting from one end of the tool body and spaced from the axis thereof for reception in the spaced apertures of the stud adapter section, a tool head adjacent an opposite end of the tool body for engagement by a drive member for rotating the tool body about the axis and a layer of a material about one end thereof for engaging the stud adapter section and preventing galling thereof.
In a further preferred embodiment according to the present invention, there is provided a method of inserting an adapter section of a sectional terminal stud into the radial bore of a dynamoelectric machine having a rotor, a bore connector extending generally in an axial direction along a portion of the rotor and having a generally radially outwardly opening aperture, the terminal stud including an outer section, the stud adapter section having a male projection at one end and a recess at an opposite end and a flexible electrical connector in the recess, comprising the steps of (a) disposing an end of an elongated tool into the recess into engagement with the electrical connector to frictionally retain the stud adapter section on the end of the tool, (b) inserting the stud adapter section into the radial bore of the rotor to engage the male projection thereof in the aperture of the bore connector and (c) withdrawing the tool from within the recess of the stud adapter section and the radial bore, leaving the stud adapter section engaged with the bore connector.